Method of control for electric motors.



UNITED STATES PATENT OFFICE.

NORMAN W. STORER, OF PITTSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & 'MANUFACTURING COMPANY, A CORPORATION PENNSYLVANIA.

vMETHOD OF CONTROL FOR ELECTRIC MOTORS.'

Specification of Letters Patent.

Patented uly 2, 1907l I To all whom 'it mayr concern:

Beit known that I, N onu'nn' W. Sronnn, a citizen ofl the United States, and a resident of Pittsburg, in the county of Allegheny'and State of Pennsylvania, have .invented a new and useful Improvement in Methods of vControl for Electric Motors, of which the following is a specification. v

My invention relates to methods of control for electric motors, and it 4has for its object to provide a method whereby the elciency of operation of the system which proved.

In practicing the series-parallel method of control oi electric motors, the motors have usually been accelerated at 'a substantially constant rate until full voltage was applied to them. The result has been that each motor 'has been supplied with the same average amount of current whether the motors were connected'in series or in parallel relation.A U nder these conditions, twice as'much current has been supplied to aahaving two motors when the motors were connected in parallel relation as-has been supplied when the motors were connectedin series. Since it is the maximum amount oi current that must be delivered which determines the capacity of many stations, it is evidently desirable to limit the fluctuations in the amount of .current required to the minimum whicli will permit'of fulfilment of the required service co'nditions. This. is particularly desirable in railway. systems that operate a sn Ll number of cars, only one of which may, perhaps, be .Applied at a time by any sub-station.

In the practice oi my invention, the avi rage amount of currentsupplied to a car during acceleration may be maintainedsubstantially constant and may be prevented from exceeding a predetermined amount whether the motors are connected in series or -in parallel, thereby preventing extreme fluctuations-in the amount oi current that must be delivered by a sub-station.

While my method may be practiced in all systems oi control in 'which the circ uit relations of the motors may be changed, .it is most advantageously practiced in systems in which the operation of a plurality of switches y lhcated in the motor circuits may be governed by means oi a master switch and in which the switches operate successively and automatically as the motors accelerate in speed, the rate 6i acceleratign being dependent upon the amount of current traversingthe motor circuits. The switches in such systems are usually provided with magnet windings, which serve, directly or indi- 50,'rectly, to maintain the switches in closed circuit positions after they have once been closed. It is in connection with such a system that I shall explain my invention,

Means have heretofore been providedior preventing further operation oi the motor-controlling switches when the clnrent supplied to the motors exceeds a predetermined amount, such means comprising a limit switch the controlling magnet winding oi which is connected in circuit with both of the motors, while the motors are connected in series, and in circuit with only one of the motors when the motors are connected in parallel. Under ordinary conditions, such means have served only to limit the amount oi current which may be supplied to one oi the motors when the motors are connected in parallel and, consequently, in the use of such systems, twice as much current may be supplied to a car when the motors are connected in parallel as when they are connected in series. In the employment of my invention in connection with such a system, a limit switch is provided, the controlling magnet winding of which is always connected in circuit with both of the motors and serves to limit the current that may be supplied to the motors to substantially the same amount, whether they are connected in series or in parallel.

In the practice oi the ordinary series-parallel method of control, theamount of current supplied to the motors' may increase greatly when the motors are changed from series to parallel relations, and my method contemplates iurther the prevention of a change in the circuit relations o the motors until they have attained such a speed, while connected in series, that the amount of current which will ordinarily be supplied to them immediately after being connected in p xrallel will not exceed the predetermined maximum amount.

Thesingle iigure of the accompanying drawing` is a diagram oi a system embodying my inventio *i Energy may be supplied from a trolley conductor l and a track rail 2 to motors 3 and 4, the circii i conditions and connections of whichA are governed *y means of switches 5, 6, 7, 8, 9 and l0. Switches 5 to l0, inclusive, are providedwith operating or -controlling magnet windings l1, l2, 13, I4, l5 and 1G, respectively, which are adapted to be supplied with energy from any suitable source, such as a battery 17. The circuits of the operating or controlling magnet windings are governed, primarily, by means of a master switch 18 and, secondarily, by means of interlocking switches'l9, 20, 2l, 22 and 23, which insure closure of the switches in a predeterminedV order. The switches to l0, inclusive,

The circuits of the retaining muguet unir ings are governed, primarily, by the'mnste'r tclil end, secondurily, by means oi interlocking switches O, 3l

and 32 that are operatedr` respective1 by of switches (i, 7, 9 and 10 and that serve to insure energizing oi the retaining magnet windings in e pre/loten mined order.

Permanently connected in circuit with t ie motors, eremugnet windings 33 und 3i that control the opent- 'tion of switches 35 and 36, respectively, 'lhe switch 35 is located in the circuit with the operating nmgn et windingsof switches to l0, inclusive, and is adapted to be opened when the current supplied to the motors exceeds o predetermined amount, regardless of whether the motors are connected in series or in parallel relation,

The switc'nBG is located inthe circuit of the controlling magnet windings l5 `and 16 and, when open, prevents closing of the switches 9 and. l() for the purpose ot connecting the motors in parallel. relation. The amount of current Which the switch 86 muy be set to open should be less then that at which the switch 35 will operste, inorder that current may not be supplied to the The function that is performed by the switch 36 oi delaying oper on oi the switches which connect the motors in parallel until the curren supplied has fallen below a. predetermined amount, may also be served by a dash-pot (not shown) attached to the switch 9, or any other suitable means muy oe employed ior this purpose.

In the operation of the system, the master switch l8- is first moved to position a sind the switches 5 und 6 close, thus connecting the motors in series with each other lind with e, resistance 37. li the muster switch is moved to position b, the switch fi will close and portion oi the resistance 137 will be shuntod, li the muster switch is moved tovposition c, switch will close and the remaining portion or' the resistance :i7 will be shuntcd.v li the muster switch is moved to position d, switch 9 will close, switches 6, 7 and S will open sind switch lll will close und the motors will then be connected in parallel with the resistance 37 in circuit. li the master switch is moved to positions e und f, vthe switches l und S will close in succession und .the resistanco 37 will be sl ited.

li thomas1; 7itch is moyed directly to the position c, the switches will. close mitomstically. in the order previously stated, until the motors nrc s. uectod in series with no resistancein the circuit, und .i the muster switch is then moved to the position j', the switches will close automatically, in the order previously stated, until the motors are connected in parallel relation with no resistance in circuit, .the order ol closure` of the switches being governedi by meuns of the interlocking switches. li the muster switch moved directly to position f, the switches will close automatically in the proper order untn the motors nre connected in iull purnllel relation.

Since the details of operation oi the system und the specific functions ol' the interlockingr switches .loi-n1 no port ol' my present invention, and since the system op crates` in most respects, in u manner substantially similar to that described in Patent No. 773,833, granted "rio *cmber l, i904, to George.Westinghousm'upon :in application l'iled by George lfestinghouse und Lo ui s M. ilspinwell, l deem it unnecessaryto dcscribethe control circuits more particularly.

When the switch 35 is open, the circuits of the operatp ing magnet windings 'of the switches 6 to 10, inclusive, are open, While one or more oi the retaining `magnet windings 24 to 28, inclusive, may loe energized und thus maintain the circuit conditions as they were previous to opening oi the switch 35. Normal op' eration oi the system muy be resumed only after the current delivered to the motors has lullen below the predetermined amount which caused the switch 35 to open. As before described, thc switches 9 'und l0 which connect the motors cannot be closed While the switch 36 is open; that is, while the current supplied to the motors when connected in series exceeds u. predetermined amc-unt lessthan the predetermined niniount which will cause the switch 35 to open.

`While l have shown my invention as practiced in u. system oi control ior two motors, it will be understood that it may also be applied to systems of control or four or more motors, in which the number, construction und arrangement of the control switches :ind the circuits therefor may be modified, Within reasonable limits, to meet 'the conditions imposed by the employment of :t greater number o motors oi' otherwise. By suitable modifications of the governing circuits, my invention may also be practiced in combination with any other I claim' as myrinvention:

1. The method of operating a plurality of electric motors which consists in connecting; them first ln series relzbl tion und then in parallel relation, and limiting-the amount of current taken from the supply circuit rto substantially the same maximum for parallel 'operation as "that required for series operation of the motors.

12. The method of operating u plurality of electric motors which consists in connecting tliein first in series re lation und then in parallel relation, and Illnitus the amount of current taken by all of the motors when connected ln parallel to a maximum that does not mute'ri'zillyl The method of operating a plurality of electric mofrom the su ly circuit to substantially' the same maximurn for both relations of the motors.

6. The method of operating a. plurality ai' 'electric motors which consists in adjusting "che circuit relations thereof, und limiting the amount ot' current tn from 'the supply c' :uit to snbszmtinlly the same maxin'yum for all of the circuit relations of. the motors.

in testimony whereof, I have hereunto subscribe my nume tifs Sth day of July, 1905.

NoRMAN W. STORM-L 

